Spent fuel pool

Spent fuel pools (SFP) are storage pools (or "ponds" in the United Kingdom) for spent fuel from nuclear reactors. They are typically 40 or more feet (12 m) deep, with the bottom 14 feet (4.3 m) equipped with storage racks designed to hold fuel assemblies removed from reactors. A reactor's local pool is specially designed for the reactor in which the fuel was used and is situated at the reactor site. Such pools are used for short-term cooling of the fuel rods. This allows short-lived isotopes to decay and thus reduces the ionizing radiation and decay heat emanating from the rods. The water cools the fuel and provides radiological protection from its radiation. Pools also exist on sites remote from reactors, for longer term storage such as the Independent Spent Fuel Storage Installation (ISFSI), located at the Morris Operation, or as a production buffer for 10 to 20 years before being sent for reprocessing or dry cask storage. While only about 20 feet (about 6 m) of water is needed to keep radiation levels below acceptable levels, the extra depth provides a safety margin and allows fuel assemblies to be manipulated without special shielding to protect the operators. About a quarter to a third of the total fuel load of a reactor is removed from the core every 12 to 24 months and replaced with fresh fuel. Spent fuel rods generate intense heat and dangerous radiation that must be contained. Fuel is moved from the reactor and manipulated in the pool generally by automated handling systems, although some manual systems are still in use. The fuel bundles fresh from the core are normally segregated for several months for initial cooling before being sorted into other parts of the pool to wait for final disposal. Metal racks keep the fuel in controlled positions for physical protection and for ease of tracking and rearrangement. High-density racks also incorporate boron-10, often as boron carbide (Metamic, Boraflex, Boral, Tetrabor and Carborundum) or other neutron-absorbing material to ensure subcriticality.